SEBWIN-1146: Fixed deadlock introduced with runtime integrity monitoring.

Author: dbuechel

SafeExamBrowser.Client/Responsibilities/IntegrityResponsibility.cs

@@ -9,8 +9,7 @@
 using System;
 using System.Linq;
 using System.Threading.Tasks;
-using System.Windows;
-using System.Windows.Threading;
+using System.Timers;
 using SafeExamBrowser.Client.Contracts;
 using SafeExamBrowser.Configuration.Contracts.Integrity;
 using SafeExamBrowser.I18n.Contracts;
@@ -23,15 +22,15 @@ internal class IntegrityResponsibility : ClientResponsibility
 	{
 		private readonly ICoordinator coordinator;
 		private readonly IText text;
-		private readonly DispatcherTimer timer;
+		private readonly Timer timer;
 
 		private IIntegrityModule IntegrityModule => Context.IntegrityModule;
 
 		public IntegrityResponsibility(ClientContext context, ICoordinator coordinator, ILogger logger, IText text) : base(context, logger)
 		{
 			this.coordinator = coordinator;
 			this.text = text;
-			this.timer = new DispatcherTimer(DispatcherPriority.Normal, Application.Current.Dispatcher);
+			this.timer = new Timer();
 		}
 
 		public override void Assume(ClientTask task)
@@ -65,18 +64,25 @@ private void ScheduleIntegrityVerification()
 
 		private void StartIntegrityMonitoring()
 		{
-			timer.Interval = TimeSpan.FromSeconds(5);
-			timer.Tick += Timer_Tick;
+			const int FIVE_SECONDS = 5000;
+
+			timer.AutoReset = false;
+			timer.Interval = FIVE_SECONDS;
+			timer.Elapsed += Timer_Elapsed;
 			timer.Start();
+
+			Logger.Info("Started monitoring runtime integrity.");
 		}
 
 		private void StopIntegrityMonitoring()
 		{
 			timer.Stop();
-			timer.Tick -= Timer_Tick;
+			timer.Elapsed -= Timer_Elapsed;
+
+			Logger.Info("Stopped monitoring runtime integrity.");
 		}
 
-		private void Timer_Tick(object sender, EventArgs e)
+		private void Timer_Elapsed(object sender, ElapsedEventArgs e)
 		{
 			Logger.Info("Attempting to verify runtime integrity...");
 
@@ -88,6 +94,8 @@ private void Timer_Tick(object sender, EventArgs e)
 			{
 				Logger.Warn("Failed to verify runtime integrity!");
 			}
+
+			timer.Start();
 		}
 
 		private void UpdateSessionIntegrity()

SafeExamBrowser.Runtime/Responsibilities/IntegrityResponsibility.cs

@@ -8,8 +8,7 @@
 
 using System;
 using System.Threading.Tasks;
-using System.Windows;
-using System.Windows.Threading;
+using System.Timers;
 using SafeExamBrowser.Configuration.Contracts.Integrity;
 using SafeExamBrowser.Logging.Contracts;
 
@@ -19,7 +18,7 @@ internal class IntegrityResponsibility : RuntimeResponsibility
 	{
 		private readonly IIntegrityModule integrityModule;
 		private readonly Action shutdown;
-		private readonly DispatcherTimer timer;
+		private readonly Timer timer;
 
 		public IntegrityResponsibility(
 			IIntegrityModule integrityModule,
@@ -29,7 +28,7 @@ public IntegrityResponsibility(
 		{
 			this.integrityModule = integrityModule;
 			this.shutdown = shutdown;
-			this.timer = new DispatcherTimer(DispatcherPriority.Normal, Application.Current.Dispatcher);
+			this.timer = new Timer();
 		}
 
 		public override void Assume(RuntimeTask task)
@@ -47,18 +46,25 @@ public override void Assume(RuntimeTask task)
 
 		private void StartIntegrityMonitoring()
 		{
-			timer.Interval = TimeSpan.FromSeconds(5);
-			timer.Tick += Timer_Tick;
+			const int FIVE_SECONDS = 5000;
+
+			timer.AutoReset = false;
+			timer.Interval = FIVE_SECONDS;
+			timer.Elapsed += Timer_Elapsed;
 			timer.Start();
+
+			Logger.Info("Started monitoring runtime integrity.");
 		}
 
 		private void StopIntegrityMonitoring()
 		{
 			timer.Stop();
-			timer.Tick -= Timer_Tick;
+			timer.Elapsed -= Timer_Elapsed;
+
+			Logger.Info("Stopped monitoring runtime integrity.");
 		}
 
-		private void Timer_Tick(object sender, EventArgs e)
+		private void Timer_Elapsed(object sender, ElapsedEventArgs e)
 		{
 			Logger.Info("Attempting to verify runtime integrity...");
 
@@ -70,6 +76,8 @@ private void Timer_Tick(object sender, EventArgs e)
 			{
 				Logger.Warn("Failed to verify runtime integrity!");
 			}
+
+			timer.Start();
 		}
 
 		private void HandleRuntimeIntegrityStatus(bool isValid)
@@ -82,6 +90,8 @@ private void HandleRuntimeIntegrityStatus(bool isValid)
 			{
 				Logger.Error("Runtime integrity is compromised!");
 
+				StopIntegrityMonitoring();
+
 				Task.Run(() =>
 				{
 					if (SessionIsRunning)